When a projector is positioned, if an optical axis extending through the projector's lens is not orthogonal to a projection screen, then keystone distortion occurs. The keystone distortion can be one-dimensional (e.g., vertical or horizontal offset) or two-dimensional (e.g., vertical and horizontal offset). Keystone distortion occurs when: (a) a projected image plane is not parallel to the screen plane; and (b) the optical axis is not orthogonal to the screen plane. If keystone distortion is readily detected by humans, then it can detract from apparent quality of the projected image.